How to do HiFi AM on the Kenwood TS-950SDX

Written by:

Bill Paul N1GPT

The TS-950SDX is well known for being able to produce outstanding HiFi SSB audio. Using a couple of special power-on menu options, it's possible to achieve up to 6.7Khz of audio frequency response. However, due to a design quirk, once you set the LPF option to 'off' to open up the high end response, the DSP will no longer generate a carrier when the radio is set for AM mode. This prevents the operator from achieving Hi-Fi sound on AM.

It turns out though that you can make the radio transmit in HiFi mode in AM, if you trick it. I've discovered two ways so far. The first is to set the LPF menu option to 3100Hz, then begin transmitting in AM, and then change the menu option to 'off' without releasing the key. The other is to set the LPF menu option to 'off,' then begin transmitting in AM, and then switch to either LSB or USB mode and then back to AM mode again. (Using FM instead of LSB or USB also works. CW does not.)

The only problem is that you have to do this every time you transmit, which makes operation clumsy. Fortunately, I've found two ways to address this. One is to use an external computer assist program to shift modes automatically when the user engages the transmitter. The other is to patch the firmware for the main CPU so that it works around the DSP's glitchy behavior internally. This page provides links to both solutions.

The software-only solution has the advantage that no modifications to the radio are required at all: if you have your radio connected to a computer already, you just need to run the program and leave it going in the background. However it has a few drawbacks: you can't use any other CAT software while the program is running, and it's a little slow: it may take a half second or so after you press the transmit button on the radio before the program senses it and swaps modes.

The firmware patch solution has no operational drawbacks and is the most seamless solution (the radio just works), but requires making a new firmware EPROM and opening up the radio to install it.

To download the CAT utility, click here:

Kenwood TS-950SDX AM DSP CAT utility

To download the modified firmware, click here:

Patched Kenwood TS-950SDX HiFi AM firmware